Strange data from Flat Spot load workup

[tddeangelo]

I took my Whelen to the range today to run some charges for flatspot load development.

It's not really what I thought I'd get, based on what I've seen folks post here, but I'm guessing there's a learning opportunity here, so I'll post the data for others who know more to check out and see if anyone has any ideas/pointers.

I'm running IMR4320 and a 250gr Nosler Partition with a WLR primer in Hornady brass. I bumped my shoulders back 0.005" from a fired case. QuickLoad predicted 2600fps at 58.0gr charge weight, and with a 63,000PSI threshold, showed a max coming at 58.8gr. I seated to 3.365" OAL, as that'll run in my magazine well...barely. It'll run, but I'd guess rounds in the mag when the rifle's fired might get the points flattened slightly.

Anyway.... data set:

56.0 = 2428
56.2 = 2448
56.4 = 2458
56.6 = 2445
56.8 = 2471
57.0 = 2461
57.2 = 2465
57.4 = 2441
57.6 = 2480
57.8 = 2475
58.0 = 2468


I ran out of daylight, but I have loads made up for 58.2, 58.4, 58.6, and 58.8gr charges. Just didn't get to shoot them.

I ran one of my rounds with my established load in that rifle, which is a Speer 250gr HotCor on 58.0gr IMR4320. It read 2583.

I had my new MagnetoSpeed out today, and some may be my newness with the MS unit, but that speed on the established load tracks close to what light chrony's have read on that load. I've had them read 2525-2550 on that load, so a reading of 2583 isn't shocking.

I ran a 150PT load on the 270 and that came in at 2800-2823, also about what I expected. I sort of was hoping it made high 2800's, but I was suspecting it wouldn't.

Based on that, it seems like the MS is generating reasonable data...?

But if that's so, the data I got today is odd. It almost looks like a huge flatspot from 56.8 to 58.0.

That seems HUGE though....?

Also seems weird that the Speer runs 100fps faster than the PT?

Unexpected results are generally a pain, but I also find I usually learn something from them eventually, so I'm curious now.

 

[jimbires]

Tom , it looks like things are staying to flat , 52 FPS max spread in 2.0 gr of powder . what scale are you using , and could you double check it with another scale ? I'm thinking I'm going to set up my 10-10 scale to double check my digital scale the next time I run a flat spot work up . just to try and double check powder weight . another thought , is this brass all from the same lot ? all fired about the same number of times ?

 

[tddeangelo]

Hi Jim,

Yep, all same lot and firings.

One thing I just thought of....I was fighting a losing battle with my Hornady Prep center till I realized I was using the wrong shell holder. Doh. So I have maybe 10/1000 variance in trim length on those brass.

I ran charges on my ChargeMaster. Good idea on a double check. I have a balance scale. I'll do that next time to be certain I'm getting what I am thinking in getting from the CM.

 

[truck driver]

Tom I think you need to finish the test. You are only showing the lower end and the best nodes usually comes from some where in the middle of the run to just below max from what I have seen with my test.
I'm know expert and just learning how to read the nodes myself but think you need to discard everything below 56.8grs if you are dropping back 2grs and working up to max .2grs at a time.
I'm also not sure why you're seeing 115fps difference between Speer and Nosler bullets unless it is do to a difference in jacket material with the Speer being harder causing more pressure.
I think Dewey will be along and will know more than I do and help to explain what your seeing.

 

[tddeangelo]

QL predicted 58.8 as my max, which prompted me to start where I did.

With the speeds it's producing, it may let me go higher than that safely.

I'll run more soon and see what I get. I may build 57.0-59.0 and double check weights with my balance scale. Then rerun for speeds and see what I see. What puzzles me is that difference in speed from the Speer to PT.

 

[truck driver]

I sent you an email instead of posting a long post here. Start 1.5-2.0grs below max and work up 10 loads. if 58.8 is max the 1.5gr run will put you at 59.1grs on the top end.
Different bullet jacket alloy could be causing the velocity difference.

 

[jimbires]

.010 in case length will not give you any problems like this .


when I switch bullets , or powders , I either clean the barrel , or I'll shoot 2 or 4 shots of the new load to get the bbl rid of any left overs from the previous components . I've been told that you can get unexplained happenings for a couple of shots when changing any components without cleaning in between . maybe this is what happened to the speer velocity being 100fps higher than the nosler . just a guess .



let us know what you figure out on this work up , I'm interested .

 

[tddeangelo]

Makes sense.

To hold to changing one variable at a time, I'll add the check with the balance scale into my procedure.

If that makes no change, I'll do a full cleaning regimen.

I'll post as I get more data points.

 

[tddeangelo]

Ok, so some more data....

I ran 56.8 to 59.4 I still had 58.2, 58.4, 58.6, and 58.8 from my batch yesterday. All the rest I loaded today. I had my ChargeMaster throw each one, then I put it on my Lyman balance scale. Out of the 10 loads I made today, only one wasn't SPOT ON when I put it on my balance scale. That was off by about 4 or 5 powder kernels. The CM seems to be tracking pretty good.

I attached my data sheet from the range. Left column is today's data. Middle column is yesterday's data. Right column is the difference for the charges from yesterday to today where I had speeds for the same load from each day.

As you can see, the speeds vary a bit. One thing, though...when I did the QL data, I forgot to change the OAL from my Speer load to the depth I seated the PT's, which wasn't as deep as the speers. When I made the change the COAL, the QL numbers literally snapped right into place, almost.

Now I think we're a little closer to seeing some good trends. Both 2600+ shots I think were caused by me forgetting to check the MS unit mounting. One time it fell off, the other time I think it was close.

 

[tddeangelo]

And yes, I did the math in my head for the difference in speeds. Some are not quite correct. Whoops. :lol:

 

[SJB358]

This seems even across the board. I believe you are on to something at the 2550 mark. I'd be okay with that big monster honking out at that speed.

 

[tddeangelo]

I'm curious where more powder goes. There's room from what I see in speeds vs pressures in QL.

I'm curious if it gets more consistent as the charge goes up. Max looks to be 61.4 with speeds over 2600. Not like 2550 wouldn't kill about anything, though.

 

[SJB358]

I'm curious where more powder goes. There's room from what I see in speeds vs pressures in QL.

I'm curious if it gets more consistent as the charge goes up. Max looks to be 61.4 with speeds over 2600. Not like 2550 wouldn't kill about anything, though.

Only one way to tell. Great thing about the MS, you can do it over numerous days and not sweat lighting or other stuff.

 

[tddeangelo]

Yep. I'll run more charges later this week and then pick some charges to work with.